2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset
32 std::atomic<Score> Eval::Contempt;
36 enum Tracing { NO_TRACE, TRACE };
38 enum Term { // The first 8 entries are reserved for PieceType
39 MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB
42 Score scores[TERM_NB][COLOR_NB];
44 double to_cp(Value v) { return double(v) / PawnValueEg; }
46 void add(int idx, Color c, Score s) {
50 void add(int idx, Score w, Score b = SCORE_ZERO) {
51 scores[idx][WHITE] = w;
52 scores[idx][BLACK] = b;
55 std::ostream& operator<<(std::ostream& os, Score s) {
56 os << std::setw(5) << to_cp(mg_value(s)) << " "
57 << std::setw(5) << to_cp(eg_value(s));
61 std::ostream& operator<<(std::ostream& os, Term t) {
63 if (t == MATERIAL || t == IMBALANCE || t == INITIATIVE || t == TOTAL)
64 os << " ---- ----" << " | " << " ---- ----";
66 os << scores[t][WHITE] << " | " << scores[t][BLACK];
68 os << " | " << scores[t][WHITE] - scores[t][BLACK] << "\n";
73 using namespace Trace;
77 const Bitboard QueenSide = FileABB | FileBBB | FileCBB | FileDBB;
78 const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
79 const Bitboard KingSide = FileEBB | FileFBB | FileGBB | FileHBB;
80 const Bitboard Center = (FileDBB | FileEBB) & (Rank4BB | Rank5BB);
82 const Bitboard KingFlank[FILE_NB] = {
83 QueenSide, QueenSide, QueenSide,
84 CenterFiles, CenterFiles,
85 KingSide, KingSide, KingSide
88 // Threshold for lazy and space evaluation
89 const Value LazyThreshold = Value(1500);
90 const Value SpaceThreshold = Value(12222);
92 // KingAttackWeights[PieceType] contains king attack weights by piece type
93 const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
95 // Penalties for enemy's safe checks
96 const int QueenSafeCheck = 780;
97 const int RookSafeCheck = 880;
98 const int BishopSafeCheck = 435;
99 const int KnightSafeCheck = 790;
101 #define S(mg, eg) make_score(mg, eg)
103 // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
104 // indexed by piece type and number of attacked squares in the mobility area.
105 const Score MobilityBonus[][32] = {
106 { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S( 6, 5), S( 14, 12), // Knights
107 S( 22, 26), S( 29, 29), S( 36, 29) },
108 { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
109 S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
110 S( 91, 88), S( 98, 97) },
111 { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
112 S( 9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
113 S( 46,166), S( 48,169), S( 58,171) },
114 { S(-39,-36), S(-21,-15), S( 3, 8), S( 3, 18), S( 14, 34), S( 22, 54), // Queens
115 S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
116 S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
117 S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
118 S(106,184), S(109,191), S(113,206), S(116,212) }
121 // Outpost[knight/bishop][supported by pawn] contains bonuses for minor
122 // pieces if they occupy or can reach an outpost square, bigger if that
123 // square is supported by a pawn.
124 const Score Outpost[][2] = {
125 { S(22, 6), S(36,12) }, // Knight
126 { S( 9, 2), S(15, 5) } // Bishop
129 // RookOnFile[semiopen/open] contains bonuses for each rook when there is
130 // no (friendly) pawn on the rook file.
131 const Score RookOnFile[] = { S(20, 7), S(45, 20) };
133 // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to
134 // which piece type attacks which one. Attacks on lesser pieces which are
135 // pawn-defended are not considered.
136 const Score ThreatByMinor[PIECE_TYPE_NB] = {
137 S(0, 0), S(0, 31), S(39, 42), S(57, 44), S(68, 112), S(47, 120)
140 const Score ThreatByRook[PIECE_TYPE_NB] = {
141 S(0, 0), S(0, 24), S(38, 71), S(38, 61), S(0, 38), S(36, 38)
144 // ThreatByKing[on one/on many] contains bonuses for king attacks on
145 // pawns or pieces which are not pawn-defended.
146 const Score ThreatByKing[] = { S(3, 65), S(9, 145) };
148 // PassedRank[Rank] contains a bonus according to the rank of a passed pawn
149 const Score PassedRank[RANK_NB] = {
150 S(0, 0), S(5, 7), S(5, 13), S(32, 42), S(70, 70), S(172, 170), S(217, 269)
153 // PassedFile[File] contains a bonus according to the file of a passed pawn
154 const Score PassedFile[FILE_NB] = {
155 S( 9, 10), S(2, 10), S(1, -8), S(-20,-12),
156 S(-20,-12), S(1, -8), S(2, 10), S( 9, 10)
159 // PassedDanger[Rank] contains a term to weight the passed score
160 const int PassedDanger[RANK_NB] = { 0, 0, 0, 2, 7, 12, 19 };
162 // KingProtector[PieceType-2] contains a penalty according to distance from king
163 const Score KingProtector[] = { S(3, 5), S(4, 3), S(3, 0), S(1, -1) };
165 // Assorted bonuses and penalties
166 const Score BishopPawns = S( 8, 12);
167 const Score CloseEnemies = S( 7, 0);
168 const Score Connectivity = S( 3, 1);
169 const Score Hanging = S( 52, 30);
170 const Score HinderPassedPawn = S( 8, 1);
171 const Score KnightOnQueen = S( 21, 11);
172 const Score LongRangedBishop = S( 22, 0);
173 const Score MinorBehindPawn = S( 16, 0);
174 const Score PawnlessFlank = S( 20, 80);
175 const Score RookOnPawn = S( 8, 24);
176 const Score SliderOnQueen = S( 42, 21);
177 const Score ThreatByPawnPush = S( 47, 26);
178 const Score ThreatByRank = S( 16, 3);
179 const Score ThreatBySafePawn = S(175,168);
180 const Score TrappedBishopA1H1 = S( 50, 50);
181 const Score TrappedRook = S( 92, 0);
182 const Score WeakQueen = S( 50, 10);
183 const Score WeakUnopposedPawn = S( 5, 25);
187 // Evaluation class computes and stores attacks tables and other working data
192 Evaluation() = delete;
193 explicit Evaluation(const Position& p) : pos(p) {}
194 Evaluation& operator=(const Evaluation&) = delete;
198 template<Color Us> void initialize();
199 template<Color Us, PieceType Pt> Score pieces();
200 template<Color Us> Score king() const;
201 template<Color Us> Score threats() const;
202 template<Color Us> Score passed() const;
203 template<Color Us> Score space() const;
204 ScaleFactor scale_factor(Value eg) const;
205 Score initiative(Value eg) const;
210 Bitboard mobilityArea[COLOR_NB];
211 Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };
213 // attackedBy[color][piece type] is a bitboard representing all squares
214 // attacked by a given color and piece type. Special "piece types" which
215 // is also calculated is ALL_PIECES.
216 Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];
218 // attackedBy2[color] are the squares attacked by 2 pieces of a given color,
219 // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through
220 // pawn or squares attacked by 2 pawns are not explicitly added.
221 Bitboard attackedBy2[COLOR_NB];
223 // kingRing[color] are the squares adjacent to the king, plus (only for a
224 // king on its first rank) the squares two ranks in front. For instance,
225 // if black's king is on g8, kingRing[BLACK] is f8, h8, f7, g7, h7, f6, g6
226 // and h6. It is set to 0 when king safety evaluation is skipped.
227 Bitboard kingRing[COLOR_NB];
229 // kingAttackersCount[color] is the number of pieces of the given color
230 // which attack a square in the kingRing of the enemy king.
231 int kingAttackersCount[COLOR_NB];
233 // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the
234 // given color which attack a square in the kingRing of the enemy king. The
235 // weights of the individual piece types are given by the elements in the
236 // KingAttackWeights array.
237 int kingAttackersWeight[COLOR_NB];
239 // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given
240 // color to squares directly adjacent to the enemy king. Pieces which attack
241 // more than one square are counted multiple times. For instance, if there is
242 // a white knight on g5 and black's king is on g8, this white knight adds 2
243 // to kingAdjacentZoneAttacksCount[WHITE].
244 int kingAdjacentZoneAttacksCount[COLOR_NB];
248 // Evaluation::initialize() computes king and pawn attacks, and the king ring
249 // bitboard for a given color. This is done at the beginning of the evaluation.
250 template<Tracing T> template<Color Us>
251 void Evaluation<T>::initialize() {
253 const Color Them = (Us == WHITE ? BLACK : WHITE);
254 const Direction Up = (Us == WHITE ? NORTH : SOUTH);
255 const Direction Down = (Us == WHITE ? SOUTH : NORTH);
256 const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);
258 // Find our pawns that are blocked or on the first two ranks
259 Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);
261 // Squares occupied by those pawns, by our king, or controlled by enemy pawns
262 // are excluded from the mobility area.
263 mobilityArea[Us] = ~(b | pos.square<KING>(Us) | pe->pawn_attacks(Them));
265 // Initialise attackedBy bitboards for kings and pawns
266 attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));
267 attackedBy[Us][PAWN] = pe->pawn_attacks(Us);
268 attackedBy[Us][ALL_PIECES] = attackedBy[Us][KING] | attackedBy[Us][PAWN];
269 attackedBy2[Us] = attackedBy[Us][KING] & attackedBy[Us][PAWN];
271 // Init our king safety tables only if we are going to use them
272 if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)
274 kingRing[Us] = attackedBy[Us][KING];
275 if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
276 kingRing[Us] |= shift<Up>(kingRing[Us]);
278 kingAttackersCount[Them] = popcount(attackedBy[Us][KING] & pe->pawn_attacks(Them));
279 kingAdjacentZoneAttacksCount[Them] = kingAttackersWeight[Them] = 0;
282 kingRing[Us] = kingAttackersCount[Them] = 0;
286 // Evaluation::pieces() scores pieces of a given color and type
287 template<Tracing T> template<Color Us, PieceType Pt>
288 Score Evaluation<T>::pieces() {
290 const Color Them = (Us == WHITE ? BLACK : WHITE);
291 const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
292 : Rank5BB | Rank4BB | Rank3BB);
293 const Square* pl = pos.squares<Pt>(Us);
297 Score score = SCORE_ZERO;
299 attackedBy[Us][Pt] = 0;
301 while ((s = *pl++) != SQ_NONE)
303 // Find attacked squares, including x-ray attacks for bishops and rooks
304 b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))
305 : Pt == ROOK ? attacks_bb< ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))
306 : pos.attacks_from<Pt>(s);
308 if (pos.blockers_for_king(Us) & s)
309 b &= LineBB[pos.square<KING>(Us)][s];
311 attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;
312 attackedBy[Us][Pt] |= b;
313 attackedBy[Us][ALL_PIECES] |= b;
315 if (b & kingRing[Them])
317 kingAttackersCount[Us]++;
318 kingAttackersWeight[Us] += KingAttackWeights[Pt];
319 kingAdjacentZoneAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);
322 int mob = popcount(b & mobilityArea[Us]);
324 mobility[Us] += MobilityBonus[Pt - 2][mob];
326 // Penalty if the piece is far from the king
327 score -= KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
329 if (Pt == BISHOP || Pt == KNIGHT)
331 // Bonus if piece is on an outpost square or can reach one
332 bb = OutpostRanks & ~pe->pawn_attacks_span(Them);
334 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;
336 else if (bb &= b & ~pos.pieces(Us))
337 score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];
339 // Bonus when behind a pawn
340 if ( relative_rank(Us, s) < RANK_5
341 && (pos.pieces(PAWN) & (s + pawn_push(Us))))
342 score += MinorBehindPawn;
346 // Penalty according to number of pawns on the same color square as the bishop
347 score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s);
349 // Bonus for bishop on a long diagonal which can "see" both center squares
350 if (more_than_one(Center & (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) | s)))
351 score += LongRangedBishop;
354 // An important Chess960 pattern: A cornered bishop blocked by a friendly
355 // pawn diagonally in front of it is a very serious problem, especially
356 // when that pawn is also blocked.
359 && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))
361 Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);
362 if (pos.piece_on(s + d) == make_piece(Us, PAWN))
363 score -= !pos.empty(s + d + pawn_push(Us)) ? TrappedBishopA1H1 * 4
364 : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2
371 // Bonus for aligning rook with with enemy pawns on the same rank/file
372 if (relative_rank(Us, s) >= RANK_5)
373 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
375 // Bonus for rook on an open or semi-open file
376 if (pe->semiopen_file(Us, file_of(s)))
377 score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];
379 // Penalty when trapped by the king, even more if the king cannot castle
382 File kf = file_of(pos.square<KING>(Us));
383 if ((kf < FILE_E) == (file_of(s) < kf))
384 score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));
390 // Penalty if any relative pin or discovered attack against the queen
391 Bitboard queenPinners;
392 if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, queenPinners))
397 Trace::add(Pt, Us, score);
403 // Evaluation::king() assigns bonuses and penalties to a king of a given color
404 template<Tracing T> template<Color Us>
405 Score Evaluation<T>::king() const {
407 const Color Them = (Us == WHITE ? BLACK : WHITE);
408 const Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
409 : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
411 const Square ksq = pos.square<KING>(Us);
412 Bitboard weak, b, b1, b2, safe, unsafeChecks, pinned;
414 // King shelter and enemy pawns storm
415 Score score = pe->king_safety<Us>(pos, ksq);
417 // Main king safety evaluation
418 if (kingAttackersCount[Them] > 1 - pos.count<QUEEN>(Them))
420 int kingDanger = unsafeChecks = 0;
422 // Attacked squares defended at most once by our queen or king
423 weak = attackedBy[Them][ALL_PIECES]
425 & (~attackedBy[Us][ALL_PIECES] | attackedBy[Us][KING] | attackedBy[Us][QUEEN]);
427 // Analyse the safe enemy's checks which are possible on next move
428 safe = ~pos.pieces(Them);
429 safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);
431 b1 = attacks_bb<ROOK >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
432 b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));
434 // Enemy queen safe checks
435 if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])
436 kingDanger += QueenSafeCheck;
438 b1 &= attackedBy[Them][ROOK];
439 b2 &= attackedBy[Them][BISHOP];
441 // Enemy rooks checks
443 kingDanger += RookSafeCheck;
447 // Enemy bishops checks
449 kingDanger += BishopSafeCheck;
453 // Enemy knights checks
454 b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
456 kingDanger += KnightSafeCheck;
460 // Unsafe or occupied checking squares will also be considered, as long as
461 // the square is in the attacker's mobility area.
462 unsafeChecks &= mobilityArea[Them];
463 pinned = pos.blockers_for_king(Us) & pos.pieces(Us);
465 kingDanger += kingAttackersCount[Them] * kingAttackersWeight[Them]
466 + 102 * kingAdjacentZoneAttacksCount[Them]
467 + 191 * popcount(kingRing[Us] & weak)
468 + 143 * popcount(pinned | unsafeChecks)
469 - 848 * !pos.count<QUEEN>(Them)
470 - 9 * mg_value(score) / 8
473 // Transform the kingDanger units into a Score, and subtract it from the evaluation
476 int mobilityDanger = mg_value(mobility[Them] - mobility[Us]);
477 kingDanger = std::max(0, kingDanger + mobilityDanger);
478 score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);
482 Bitboard kf = KingFlank[file_of(ksq)];
484 // Penalty when our king is on a pawnless flank
485 if (!(pos.pieces(PAWN) & kf))
486 score -= PawnlessFlank;
488 // Find the squares that opponent attacks in our king flank, and the squares
489 // which are attacked twice in that flank but not defended by our pawns.
490 b1 = attackedBy[Them][ALL_PIECES] & kf & Camp;
491 b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
493 // King tropism, to anticipate slow motion attacks on our king
494 score -= CloseEnemies * (popcount(b1) + popcount(b2));
497 Trace::add(KING, Us, score);
503 // Evaluation::threats() assigns bonuses according to the types of the
504 // attacking and the attacked pieces.
505 template<Tracing T> template<Color Us>
506 Score Evaluation<T>::threats() const {
508 const Color Them = (Us == WHITE ? BLACK : WHITE);
509 const Direction Up = (Us == WHITE ? NORTH : SOUTH);
510 const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
512 Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safeThreats;
513 Score score = SCORE_ZERO;
515 // Non-pawn enemies attacked by a pawn
516 nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
517 weak = nonPawnEnemies & attackedBy[Us][PAWN];
521 // Our safe or protected pawns
522 b = pos.pieces(Us, PAWN)
523 & (~attackedBy[Them][ALL_PIECES] | attackedBy[Us][ALL_PIECES]);
525 safeThreats = pawn_attacks_bb<Us>(b) & weak;
526 score += ThreatBySafePawn * popcount(safeThreats);
529 // Squares strongly protected by the enemy, either because they defend the
530 // square with a pawn, or because they defend the square twice and we don't.
531 stronglyProtected = attackedBy[Them][PAWN]
532 | (attackedBy2[Them] & ~attackedBy2[Us]);
534 // Non-pawn enemies, strongly protected
535 defended = nonPawnEnemies & stronglyProtected;
537 // Enemies not strongly protected and under our attack
538 weak = pos.pieces(Them) & ~stronglyProtected & attackedBy[Us][ALL_PIECES];
540 // Bonus according to the kind of attacking pieces
543 b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);
546 Square s = pop_lsb(&b);
547 score += ThreatByMinor[type_of(pos.piece_on(s))];
548 if (type_of(pos.piece_on(s)) != PAWN)
549 score += ThreatByRank * (int)relative_rank(Them, s);
552 b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];
555 Square s = pop_lsb(&b);
556 score += ThreatByRook[type_of(pos.piece_on(s))];
557 if (type_of(pos.piece_on(s)) != PAWN)
558 score += ThreatByRank * (int)relative_rank(Them, s);
561 score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);
563 b = weak & attackedBy[Us][KING];
565 score += ThreatByKing[more_than_one(b)];
568 // Bonus for enemy unopposed weak pawns
569 if (pos.pieces(Us, ROOK, QUEEN))
570 score += WeakUnopposedPawn * pe->weak_unopposed(Them);
572 // Find squares where our pawns can push on the next move
573 b = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();
574 b |= shift<Up>(b & TRank3BB) & ~pos.pieces();
576 // Keep only the squares which are not completely unsafe
577 b &= ~attackedBy[Them][PAWN]
578 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
580 // Bonus for safe pawn threats on the next move
581 b = pawn_attacks_bb<Us>(b)
583 & ~attackedBy[Us][PAWN];
585 score += ThreatByPawnPush * popcount(b);
587 // Bonus for threats on the next moves against enemy queen
588 if (pos.count<QUEEN>(Them) == 1)
590 Square s = pos.square<QUEEN>(Them);
591 safeThreats = mobilityArea[Us] & ~stronglyProtected;
593 b = attackedBy[Us][KNIGHT] & pos.attacks_from<KNIGHT>(s);
595 score += KnightOnQueen * popcount(b & safeThreats);
597 b = (attackedBy[Us][BISHOP] & pos.attacks_from<BISHOP>(s))
598 | (attackedBy[Us][ROOK ] & pos.attacks_from<ROOK >(s));
600 score += SliderOnQueen * popcount(b & safeThreats & attackedBy2[Us]);
603 // Connectivity: ensure that knights, bishops, rooks, and queens are protected
604 b = (pos.pieces(Us) ^ pos.pieces(Us, PAWN, KING)) & attackedBy[Us][ALL_PIECES];
605 score += Connectivity * popcount(b);
608 Trace::add(THREAT, Us, score);
613 // Evaluation::passed() evaluates the passed pawns and candidate passed
614 // pawns of the given color.
616 template<Tracing T> template<Color Us>
617 Score Evaluation<T>::passed() const {
619 const Color Them = (Us == WHITE ? BLACK : WHITE);
620 const Direction Up = (Us == WHITE ? NORTH : SOUTH);
622 auto king_proximity = [&](Color c, Square s) {
623 return std::min(distance(pos.square<KING>(c), s), 5);
626 Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;
627 Score score = SCORE_ZERO;
629 b = pe->passed_pawns(Us);
633 Square s = pop_lsb(&b);
635 assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));
637 bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
638 score -= HinderPassedPawn * popcount(bb);
640 int r = relative_rank(Us, s);
641 int w = PassedDanger[r];
643 Score bonus = PassedRank[r];
647 Square blockSq = s + Up;
649 // Adjust bonus based on the king's proximity
650 bonus += make_score(0, ( king_proximity(Them, blockSq) * 5
651 - king_proximity(Us, blockSq) * 2) * w);
653 // If blockSq is not the queening square then consider also a second push
655 bonus -= make_score(0, king_proximity(Us, blockSq + Up) * w);
657 // If the pawn is free to advance, then increase the bonus
658 if (pos.empty(blockSq))
660 // If there is a rook or queen attacking/defending the pawn from behind,
661 // consider all the squaresToQueen. Otherwise consider only the squares
662 // in the pawn's path attacked or occupied by the enemy.
663 defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
665 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
667 if (!(pos.pieces(Us) & bb))
668 defendedSquares &= attackedBy[Us][ALL_PIECES];
670 if (!(pos.pieces(Them) & bb))
671 unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
673 // If there aren't any enemy attacks, assign a big bonus. Otherwise
674 // assign a smaller bonus if the block square isn't attacked.
675 int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
677 // If the path to the queen is fully defended, assign a big bonus.
678 // Otherwise assign a smaller bonus if the block square is defended.
679 if (defendedSquares == squaresToQueen)
682 else if (defendedSquares & blockSq)
685 bonus += make_score(k * w, k * w);
687 else if (pos.pieces(Us) & blockSq)
688 bonus += make_score(w + r * 2, w + r * 2);
691 // Scale down bonus for candidate passers which need more than one
692 // pawn push to become passed or have a pawn in front of them.
693 if ( !pos.pawn_passed(Us, s + Up)
694 || (pos.pieces(PAWN) & forward_file_bb(Us, s)))
697 score += bonus + PassedFile[file_of(s)];
701 Trace::add(PASSED, Us, score);
707 // Evaluation::space() computes the space evaluation for a given side. The
708 // space evaluation is a simple bonus based on the number of safe squares
709 // available for minor pieces on the central four files on ranks 2--4. Safe
710 // squares one, two or three squares behind a friendly pawn are counted
711 // twice. Finally, the space bonus is multiplied by a weight. The aim is to
712 // improve play on game opening.
714 template<Tracing T> template<Color Us>
715 Score Evaluation<T>::space() const {
717 const Color Them = (Us == WHITE ? BLACK : WHITE);
718 const Bitboard SpaceMask =
719 Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
720 : CenterFiles & (Rank7BB | Rank6BB | Rank5BB);
722 if (pos.non_pawn_material() < SpaceThreshold)
725 // Find the safe squares for our pieces inside the area defined by
726 // SpaceMask. A square is unsafe if it is attacked by an enemy
727 // pawn, or if it is undefended and attacked by an enemy piece.
728 Bitboard safe = SpaceMask
729 & ~pos.pieces(Us, PAWN)
730 & ~attackedBy[Them][PAWN]
731 & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
733 // Find all squares which are at most three squares behind some friendly pawn
734 Bitboard behind = pos.pieces(Us, PAWN);
735 behind |= (Us == WHITE ? behind >> 8 : behind << 8);
736 behind |= (Us == WHITE ? behind >> 16 : behind << 16);
738 int bonus = popcount(safe) + popcount(behind & safe);
739 int weight = pos.count<ALL_PIECES>(Us) - 2 * pe->open_files();
741 Score score = make_score(bonus * weight * weight / 16, 0);
744 Trace::add(SPACE, Us, score);
750 // Evaluation::initiative() computes the initiative correction value
751 // for the position. It is a second order bonus/malus based on the
752 // known attacking/defending status of the players.
755 Score Evaluation<T>::initiative(Value eg) const {
757 int outflanking = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
758 - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
760 bool pawnsOnBothFlanks = (pos.pieces(PAWN) & QueenSide)
761 && (pos.pieces(PAWN) & KingSide);
763 // Compute the initiative bonus for the attacking side
764 int complexity = 8 * outflanking
765 + 8 * pe->pawn_asymmetry()
766 + 12 * pos.count<PAWN>()
767 + 16 * pawnsOnBothFlanks
768 + 48 * !pos.non_pawn_material()
771 // Now apply the bonus: note that we find the attacking side by extracting
772 // the sign of the endgame value, and that we carefully cap the bonus so
773 // that the endgame score will never change sign after the bonus.
774 int v = ((eg > 0) - (eg < 0)) * std::max(complexity, -abs(eg));
777 Trace::add(INITIATIVE, make_score(0, v));
779 return make_score(0, v);
783 // Evaluation::scale_factor() computes the scale factor for the winning side
786 ScaleFactor Evaluation<T>::scale_factor(Value eg) const {
788 Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
789 int sf = me->scale_factor(pos, strongSide);
791 // If we don't already have an unusual scale factor, check for certain
792 // types of endgames, and use a lower scale for those.
793 if (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN)
795 if (pos.opposite_bishops())
797 // Endgame with opposite-colored bishops and no other pieces (ignoring pawns)
798 // is almost a draw, in case of KBP vs KB, it is even more a draw.
799 if ( pos.non_pawn_material(WHITE) == BishopValueMg
800 && pos.non_pawn_material(BLACK) == BishopValueMg)
801 sf = more_than_one(pos.pieces(PAWN)) ? 31 : 9;
803 // Endgame with opposite-colored bishops, but also other pieces. Still
804 // a bit drawish, but not as drawish as with only the two bishops.
808 // Endings where weaker side can place his king in front of the enemy's
809 // pawns are drawish.
810 else if ( abs(eg) <= BishopValueEg
811 && pos.count<PAWN>(strongSide) <= 2
812 && !pos.pawn_passed(~strongSide, pos.square<KING>(~strongSide)))
813 sf = 37 + 7 * pos.count<PAWN>(strongSide);
816 return ScaleFactor(sf);
820 // Evaluation::value() is the main function of the class. It computes the various
821 // parts of the evaluation and returns the value of the position from the point
822 // of view of the side to move.
825 Value Evaluation<T>::value() {
827 assert(!pos.checkers());
829 // Probe the material hash table
830 me = Material::probe(pos);
832 // If we have a specialized evaluation function for the current material
833 // configuration, call it and return.
834 if (me->specialized_eval_exists())
835 return me->evaluate(pos);
837 // Initialize score by reading the incrementally updated scores included in
838 // the position object (material + piece square tables) and the material
839 // imbalance. Score is computed internally from the white point of view.
840 Score score = pos.psq_score() + me->imbalance() + Eval::Contempt;
842 // Probe the pawn hash table
843 pe = Pawns::probe(pos);
844 score += pe->pawn_score(WHITE) - pe->pawn_score(BLACK);
846 // Early exit if score is high
847 Value v = (mg_value(score) + eg_value(score)) / 2;
848 if (abs(v) > LazyThreshold)
849 return pos.side_to_move() == WHITE ? v : -v;
851 // Main evaluation begins here
856 // Pieces should be evaluated first (populate attack tables)
857 score += pieces<WHITE, KNIGHT>() - pieces<BLACK, KNIGHT>()
858 + pieces<WHITE, BISHOP>() - pieces<BLACK, BISHOP>()
859 + pieces<WHITE, ROOK >() - pieces<BLACK, ROOK >()
860 + pieces<WHITE, QUEEN >() - pieces<BLACK, QUEEN >();
862 score += mobility[WHITE] - mobility[BLACK];
864 score += king< WHITE>() - king< BLACK>()
865 + threats<WHITE>() - threats<BLACK>()
866 + passed< WHITE>() - passed< BLACK>()
867 + space< WHITE>() - space< BLACK>();
869 score += initiative(eg_value(score));
871 // Interpolate between a middlegame and a (scaled by 'sf') endgame score
872 ScaleFactor sf = scale_factor(eg_value(score));
873 v = mg_value(score) * int(me->game_phase())
874 + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;
876 v /= int(PHASE_MIDGAME);
878 // In case of tracing add all remaining individual evaluation terms
881 Trace::add(MATERIAL, pos.psq_score());
882 Trace::add(IMBALANCE, me->imbalance());
883 Trace::add(PAWN, pe->pawn_score(WHITE), pe->pawn_score(BLACK));
884 Trace::add(MOBILITY, mobility[WHITE], mobility[BLACK]);
885 Trace::add(TOTAL, score);
888 return (pos.side_to_move() == WHITE ? v : -v) // Side to move point of view
895 /// evaluate() is the evaluator for the outer world. It returns a static
896 /// evaluation of the position from the point of view of the side to move.
898 Value Eval::evaluate(const Position& pos) {
899 return Evaluation<NO_TRACE>(pos).value();
903 /// trace() is like evaluate(), but instead of returning a value, it returns
904 /// a string (suitable for outputting to stdout) that contains the detailed
905 /// descriptions and values of each evaluation term. Useful for debugging.
907 std::string Eval::trace(const Position& pos) {
909 std::memset(scores, 0, sizeof(scores));
911 Eval::Contempt = SCORE_ZERO; // Reset any dynamic contempt
913 Value v = Evaluation<TRACE>(pos).value();
915 v = pos.side_to_move() == WHITE ? v : -v; // Trace scores are from white's point of view
917 std::stringstream ss;
918 ss << std::showpoint << std::noshowpos << std::fixed << std::setprecision(2)
919 << " Term | White | Black | Total \n"
920 << " | MG EG | MG EG | MG EG \n"
921 << " ------------+-------------+-------------+------------\n"
922 << " Material | " << Term(MATERIAL)
923 << " Imbalance | " << Term(IMBALANCE)
924 << " Initiative | " << Term(INITIATIVE)
925 << " Pawns | " << Term(PAWN)
926 << " Knights | " << Term(KNIGHT)
927 << " Bishops | " << Term(BISHOP)
928 << " Rooks | " << Term(ROOK)
929 << " Queens | " << Term(QUEEN)
930 << " Mobility | " << Term(MOBILITY)
931 << " King safety | " << Term(KING)
932 << " Threats | " << Term(THREAT)
933 << " Passed | " << Term(PASSED)
934 << " Space | " << Term(SPACE)
935 << " ------------+-------------+-------------+------------\n"
936 << " Total | " << Term(TOTAL);
938 ss << "\nTotal evaluation: " << to_cp(v) << " (white side)\n";